Quality is delighting customers
In a mature software organization, bugs are tracked in a bug track system. The bug tracking system tracks whether the developers believe the bug has been fixed, among other things.
If you find the same bug and the bug tracking system says the developers believe the bug has been fixed, you should update the bug tracking system to indicate the bug has not been fixed. If, on the other hand, the bug tracking system says the developers have not fixed the bug, you do not need to do anything.
If the bug is preventing you from testing other things, it is your job to let someone know about it. Depending on your company's procedures, that might involve updating the bug tracking system or it might involve notifying your project lead or your manager.